Chemical vapor deposition of coatings

ABSTRACT

A metal oxide coating is applied to a hot glass surface by contacting the surface with a mixture of carrier air, vaporized solvent and a vaporized metal containing reactant. The mixture is directed against the glass through an elongated, converging slot-nozzle, the interior surfaces of which have an increasing radius of curvature towards the exit end, nozzle at a Reynolds number exceeding 2500 with the nozzle-to-glass spacing at least 1.25 times the characteristic dimension of the nozzle.

This is a division of application Ser. No. 315,393, filed Dec. 15, 1972,now U.S. Pat. No. 3,850,679.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is related to the following copending applications, allcommonly assigned, all specifically incorporated by reference herein andall filed on even date herewith: "Nozzle to Chemical Vapor Deposition ofCoatings", Ser. No. 315,394, filed Dec. 15, 1972, now U.S. Pat. No.3,888,649 by Krishna Simhan; "Coating Composition Vaporizer", Ser. No.315,395 filed Dec. 15, 1972, now abandoned, by John Sopko, and refiledas Ser. No. 533,610 on Dec. 17, 1974; Ser. No. 533,609 filed on Dec. 17,1974, which is a divisional of Ser. No. 315,395; and "Method forIncreasing Rate of Coating Using Vaporized Reactants", Ser. No. 315,384filed Dec. 15, 1972, now U.S. Pat. No. 3,852,098 by Karl H. Bloss andHarald Molketin.

This application is also related to a copending application entitled "AProcess for the Deposition of Films", Ser. No. 182,993, filed Sept. 23,1971 based on a convention priority date of Sept. 29, 1970, byHans-Jurgen Goetz, Helmut Lukas and Harald Molketin now abandoned. Thisapplication is also incorporated by reference herein.

BACKGROUND OF THE INVENTION

This invention relates to coating substrates, particularly glasssubstrates, with coatings comprised primarily of metal oxides. Thisinvention more particularly relates to contacting a hot glass surfacewith the vapors of reactants which form metal oxide coatings uponcontacting the hot glass surface.

Prior to the present invention it has been known that substrates may becoated with metal oxide coatings by contacting the substrates withsolutions comprised of metal betadiketonates and the like dissolved inappropriate solvents. See the following U.S. Patents: Mochel, U.S. Pat.No. 3,202,054, Tompkins, U.S. Pat. No. 3,081,200, Donley et al, U.S.Pat. No. 3,660,061 and Michelotti et al, U.S. Pat. No. 3,652,246. Thesepatents have disclosed to the public a number of chemical compositionswhich are suitable for the coating of glass with metal oxide coatings.In general, the techniques described for applying such coatings to glasstaught in the prior art are methods wherein a liquid spray of coatingcomposition is directed against a glass substrate surface to be coated.While these patents cover the application of particular metals or metaloxides to glass or other substrates, whether the compositions areapplied in liquid or vapor form, they each disclose, as a best mode ofapplication, contacting the substrate with the compositions in liquidform. In the development of techniques for applying vaporized coatingcompositions to heated substrates at atmospheric pressure certaindifficulties have been encountered. It has been difficult to obtaincoatings which are finely grained and uniform in appearance. Thickcoatings have been produced by contacting the substrate with a liquidspray, but it has been extremely difficult if not impossible to obtainrelatively thick films having visible light transmittances of belowabout 50% using brown vapor deposition techniques.

Vapor deposition processes have been known in the past. Most commercialembodiments of vapor deposition processes are processes carried outunder subatmospheric pressure conditions. A number of techniques haveevolved for enhancing the rate of film deposition using thesetechniques, for example, electrical fields, magnetic fields, and radiofrequency or microwave excitation have been used to increase themomentum of reactant particles in vapor coating compositions duringtheir applications. Also, wave guides have been used to direct thevapors of coating compositions to particularly confined target areas.See U.S. Pat. No. 3,114,652 to Schetky and U.S. Pat. No. 3,561,940 toScholes.

The applicants have now discovered that the uniformity of films producedby chemical vapor deposition and the rate of chemical vapor depositionor film buildup may be significantly enhanced by directing reactantcontaining vapors through a nozzle against a substrate under particularflow conditions and preferably doing so at particularnozzle-to-substrate spacings.

SUMMARY OF THE INVENTION

A vaporizable coating reactant is vaporized into a vapor phase orgaseous carrier and is delivered through a nozzle and directed against aheated substrate. The substrate and reactant temperatures are such thatupon contact with the substrate the reactant reacts to form an adherentcoating on the substrate. In order to insure rapid, efficient anduniform deposition of coating the gaseous mixture containing the coatingreactant is directed through the nozzle with a Reynolds number of atleast 2500. For high speed coating of a continuous ribbon or sheet ofglass it is preferred that the Reynolds number for the flowing gaseousmixture be at least about 5000.

The vaporizable coating reactant is generally a material which is solidor liquid at room temperature although the preferred reactants areusually solids at room temperature. The reactant may be vaporized byconventional methods, such as boiling if it is liquid, or if thereactant is a solid it may be vaporized by delivering it onto a heatedplate, by admixing it with an inert material, such as sand, and passinga heated carrier gas through the mixture or by fluidizing it with arapidly moving stream of carrier gas and heating the fluidized mixture.In the preferred embodiments of this invention the reactant is dissolvedin an appropriate solvent, and the solution is sprayed into a hotcarrier gas to vaporize the solvent and the reactant. A particularlypreferred method of vaporization and apparatus for carrying out themethod are the inventions of John Sopko and are the subject of hiscopending application Ser. No. 315,395.

The reactive coating materials which are preferred for use in thepresent invention are the pyrolizable organo metallic salts of themetals of Groups Ib through VIIb and of Group VIII of the Periodic Chartof the Elements. The preferred organo metallic salts which are employedare betadiketonates, acetates, hexoates, formates and the like. Theacetylacetonates of iron, cobalt and chromium are particularly preferredas the reactive ingredients of the present coating compositions.

While the coating reactants which are preferred for use in thisinvention are pyrolyzable materials, other kinds of reactants may alsobe employed. For example, hydrolytic reactants, such as fluorinatedbetadiketonates, particularly acetylacetonates, and metal dicumenes, maybe used. Also reactants may be employed which require the presence ofsubstantial quantities of other cooperating reactants such as oxygen,hydrogen, halogens or the like. As already indicated the preferredmethod for vaporization involves an initial step of solution so that thereactant or reactants employed should be easily dissolved in a suitablesolvent.

A variety of aliphatic and olefinic hydrocarbons and halocarbons aresuitable as solvents in carrying out the methods disclosed here. Singlecomponent solvent systems, particularly a solvent system employingmethylene chloride, are effectively employed in the present invention.Solvent systems employing two or more solvents are also found to beparticularly useful.

Some representative solvents which may be employed in carrying out thepresent invention are: methylene bromide, carbon tetrachloride, carbontetrabromide, chloroform, bromoform, 1,1,1-trichloroethane,perchlorethylene, 1,1,1-trichloroethane, dichloroiodomethane,1,1,2-tribromoethane, trichloroethylene, tribromoethylene,trichloromonofluoroethane, hexochloroethane,1,1,1,2-tetrachloro-2-chloroethane, 1,1,2-trichloro-1,2-dichloroethane,tetrafluorobromethane, hexachlorobutadiene, tetrachloroethane and thelike.

Other solvents may also be employed, particularly as mixtures of one ormore organic polar solvents, such as an alcohol containing 1 to 4 carbonatoms and one hydroxyl group and one or more aromatic non-polarcompounds, such as benzene, toluene or xylene. The volatility of thesematerials makes their use somewhat more difficult than the abovedesignated group of preferred halogenated hydrocarbons and halocarbons,but they have particular economic utility.

In the preferred practice of this invention a solution of a reactiveorgano-metallic salt in an organic solvent is directed to a vaporizingchamber. The vaporizing chamber is constructed so as to provide aheating element which heats the space surrounding the element to atemperature sufficient to vaporize the coating solution within thatspace rather than vaporizing the liquid only in contact with the heatingelement itself. A carrier gas is directed across and away from theheater to intercept the coating composition to mix with it enhancing itsrate of vaporization and to carry the vapors through the heater to thesubstrate to be coated.

Vapors of the solvent and reactive organo metallic salt are directedfrom the vaporizer chamber to an elongated manifold disposed across thewidth of a heated substrate which is to be coated. Connected to thismanifold is an elongated nozzle for directing the vapors against thesubstrate.

In a preferred embodiment, which is the subject of the copendingapplication of Krishna Simhan entitled "Nozzle for Chemical VaporDeposition of Coatings", and filed on even date herewith the elongatednozzle has as its minor cross-section a uniformly converging shape toprovide for substantially continuous acceleration of the boundary layersof vapor passing through. The major cross-sectional dimension of thenozzle is slightly less than the corresponding substrate width so that asubstrate placed in facing relation to the nozzle extends beyond themajor dimension of the nozzle at both ends thereof. This relationshipprovides for the maintenance of a substantially uniform pressure dropalong the major dimension of the nozzle and prevents the escape of adisproportionately large amount of vapors directed through the nozzle ateach end of the nozzle and thus all vapors have good contact with thesubstrate.

The face of the nozzle disposed in facing relationship to a substrate tobe coated is located in a position relative to a support for substratesto be coated such that the spacing between the nozzle face and thesurface closest thereto during coating is at least 0.5 times the widthof the nozzle at its exit. Preferably the spacing-to-nozzle width ratiois at least 0.65 and more preferably is between 0.9 and 5. In the mostpreferred embodiments the ratio is between 1.25 and 5.

The vaporizer and manifold of the coating apparatus of this inventionare operated at sufficient pressure to cause vapor flow through thenozzle at a Reynolds number of at least 2500 and preferably at leastabout 5000 in order to insure rapid, efficient and uniform deposition ofcoating.

The apparatus of this invention may be employed to apply coatings to avariety of receptive substrates. Refractory substrates, such as,glasses, glass ceramics, ceramics, porcelain clad metals and the likeare particularly amenable to coating by the present invention. Othersubstrates, such as, metals, plastics, paper and the like may also becoated according to the principles of this invention. In particular,this invention is useful to provide for the coating of flat glass withtransparent metal oxide coatings. The resulting metal oxide coated flatglass articles have found particular utility in architecturalapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial, cutaway, perspective view of the preferredapparatus for practicing the present invention, showing the flow ofvapors and other fluids employed in the practice of the invention.

FIG. 2 is a partial sectional view of the preferred vaporizer, manifoldand nozzle used in the practice of the present invention shown incombination with a sheet of float glass supported in facing relation tothe nozzle.

FIG. 3 is a partial sectional view of the preferred device of thisinvention taken along section line 3--3 of FIG. 2.

FIG. 4 is a partial sectional view of the preferred vaporizer of thisinvention taken along section line 4--4 of FIG. 3 showing the particularrelationship of the heating element therein to the chamber space withits inlets, outlets and baffling arrangement to provide for thevaporization of the coating compositions employed in this inventionwithin the space of the chamber rather than for vaporization in contactwith the heating element itself.

FIG. 5 is an enlarged sectional view of the preferred nozzle used in thepractice of this invention along with a suitable manifold fordistributing vapor to the nozzle.

FIG. 6 is a sectional view of the preferred nozzle for use in thepractice of this invention taken along section line 6--6 of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the practice of this invention it is important that the Reynoldsnumber which characterizes the flowing vapors exiting from the nozzleand being directed against the substrate being coated be greater thanabout 2500.

While a Reynolds number of at least 1700 insures that vapor flow will befully turbulent, it has now been discovered that the Reynolds numbermust be at least about 2500 in order for flow to be substantiallyuniform throughout the area of impingement against the substrate asevidenced by interferometric techniques and by the uniformity ofresulting deposits.

The Reynolds number is defined by the following classic equation: N_(Re)= W .sup.. ρ .sup.. L/η. The Reynolds number is dimensionless. Thesymbols W, ρ and η represent the flow velocity, the density and thedynamic viscosity of the flowing vapor. L is a characteristic lengthdefined at the point where the other variables are determined. Accordingto known principals of hydraulics, the characteristic dimension L whichis relevant in the defined relationship is the hydraulic diameter whichis defined as four times the cross-sectional area of the nozzle exitdivided by the wetted perimeter of the nozzle exit. The flow, densityand vapor viscosity are all characterized in the equation as the valuesof these properties at the nozzle exit.

The present invention may be more fully appreciated from a detaileddescription of the apparatus and method which follows.

Referring first to FIG. 1, a substrate, for example a sheet of glass 11,is provided for coating. The sheet of glass 11 is generally supported,preferably in a horizontal plane, and is generally supported by meanswhich can translatably move or convey the glass sheet 11 along a pathsuch as indicated by the arrow at the lower right of FIG. 1. Disposed infacing relation to the glass sheet 11 is the coating apparatus of thisinvention comprising a vaporizer assembly 12 and a vapor distributionassembly 13.

The vaporizer assembly 12 comprises a vaporizer chamber 14, which in apreferred embodiment of the invention is a cylindrical chambercontaining elements for vaporizing reactants, which elements are furtherdescribed below. The vaporizer assembly 12 further comprises means forsupplying a reactant 15 and means for supplying a carrier gas 16.

A reactant is supplied through a solution line 17 to a series ofsolution feed lines 18, each of which is connected to a spray tip 19having its discharge opening inside the vaporizer chamber 14. Thesolution line 17 is jacketed with a coolant line 20, which is dividedinto forward and return flow portions by a baffle 21. Atomization gas,preferably air, is supplied to each spray tip 19 through a series ofatomization feed lines 22, all of which are connected to an atomizationgas line 23.

The entire reactant supply means 15 is mounted onto the vaporizerchamber 14 by a series of caps 24 which surround the lines and arebolted or otherwise connected to a series of mounts 25 welded to thevaporizer chamber 14.

The carrier gas supply means 16 comprises a carrier gas manifold 26mounted on the vaporizer chamber 14 by a bracket 27. Connected to thecarrier gas manifold 26 are a series of carrier gas feed lines 28, eachconnected to a carrier gas preheater 29 which are in turn connected tothe vaporizer chamber 14 in a manner such that heated carrier gas may bedirected into the chamber. The preheaters 29 are preferably electricalresistance heaters, each having an electric power connection 30connected to a source of controlled electric power (not shown).

The vaporizer chamber 14 may be a single structure, but if it is ofextended length it is preferably of modular construction with a seriesof relatively short vaporizer chambers 14 connected end-to-end byvaporizer chamber couplings 31 which lock the individual chamberstogether.

Inside the vaporizer chamber 14 are elements for vaporizing a reactantand other materials such as a solvent. A heater 32 is mounted within thevaporizer chamber 14 in a manner such that the chamber is divided intotwo portions, one into which all incoming materials enter and one fromwhich departing vapors leave. The heater 32 is so constructed thatvapors may pass through it from the entrance portion to the exit portionof the vaporization chamber 14. A preferred heater is a fin and tubeheat exchanger having a thermally controlled heat exchange fluidsupplied to its tubes.

The heater 32 is mounted within the chamber 14 on mountings, which areefficiently also carrier gas distribution plates 33, welded or otherwiseconnected to the interior walls of the chamber 14. The carrier gasdistribution plates 33 are so shaped and connected to the chamber 14that an enclosed manifold space is formed with each plate 33 and theclosely spaced chamber wall. The carrier gas distribution plates 33 areprovided with a series of openings which permit the free flow of gas outinto the entrance portion of the vaporizer chamber 14 where it mixeswith sprayed reactant and solvent vaporizing them.

The gaseous mixture containing a reactant in the entrance portion of thevaporizer chamber 14 passes through the heater 32 which trims or finelycontrols the temperature of the mixture entering the exit portion of thevaporizer chamber 14. The heater 32 preferably has a high heat capacityrelative to the mass of flowing gaseous mixture so that thermalstability is insured.

In the exit portion of the vaporizer chamber 14 are a series of vapordischarge lines 34, extending outward through the wall of the vaporizerchamber 14 and having several inlet openings near their interior ends.The interior end of each vapor discharge line 34 is preferably coveredwith an umbrella 35 which deflects any occasional particulate material,which enters the chamber or forms in the chamber thus, preventing itfrom clogging the vapor discharge line.

Surrounding the vapor discharge lines 34 is a vapor discharge heater 36.The vapor discharge heater 36 has two cavities, an inlet cavity and areturn cavity which are connected to a recirculating heat exchange fluidsystem (not shown). During operation, hot fluid, such as oil, iscirculated through the vapor discharge heater 36 to control thetemperature of the gaseous mixture being discharged from the vaporizerchamber 14.

Connected to each vapor discharge line 34 is a coupling 37, preferably aflexible coupling, which connects the vaporizer assembly 12 to the vapordistribution assembly 13. The vapor distribution assembly 13 comprises avapor manifold or plenum 38 having two vapor channels 39 separated by adividing wall 40 and jacketed with inner and outer thermal control fluidcavities, 41 and 42. During operation, hot fluid, such as oil, iscirculated through the inner and outer cavities to control thetemperature of the gaseous mixture flowing through the vapor channels39.

The vapor channels 39 of the plenum 38 open into nozzles 43, preferablyconverging nozzles. Each nozzle is formed of opposing nozzle wallmembers 44 connected to the plenum 38. Preferably each nozzle wallmember 44 is provided with a cavity 45 through which hot fluid, such asoil, may be directed to precisely control the temperature of a gaseouscoating mixture being directed through the nozzles 43 to the substrate11.

The present coating apparatus and method may be employed in combinationwith a variety of other processes and substrates, such as paper making,metal sheet rolling and the like. The present method may be used to coata continuous sheet or a series of discrete substrates. In the preferredembodiments of this invention a continuous glass sheet is coated. Thismay be a sheet produced by the plate process, by any sheet process(Colburn, Fourcault or Pittsburgh Pennvernon Process) or by a floatprocess. The present invention can be used effectively to apply acoating to a substrate in a vertical, horizontal or otherwise orientedplane, and this feature is a particularly valuable and unique feature ofthis invention.

In a particularly preferred embodiment the present invention is used tocoat a newly formed float glass ribbon. The ribbon could be easilycoated on either major surface by the principles of this invention andthe description which follows relates to coating the top surface of theglass ribbon.

Referring now to FIGS. 2, 3 and 4 as well as to FIG. 1, the apparatus ofthis invention may be observed in a particularly preferred environment,the space between a float forming bath and an annealing lehr.

A continuous glass ribbon 11 is shown on a bath of molten metal 46, suchas molten tin, contained in a bath chamber 47 comprising refractorybottom, side and top walls 48 encased in metal sheathing 49.

The ribbon 11 is lifted from the molten metal 46 at the exit end of thebath chamber 47 on lift out rolls 50, which are suitably journaled anddriven by conventional roll driving means connected to a driving motor(not shown). Carbon blocks 51 are spring loaded and press against thebottom of the rotating rolls 50 to remove any materials which may becomedeposited on the rolls. The carbon blocks 51 are supported within arefractory extension of the bath chamber 52. Material removed from therolls which falls into this extension 52 may be easily removed on anintermittent basis.

The ribbon of glass 11 is conveyed into an annealing lehr 53 having aplurality of lehr rolls 54 therein. Conventional driving means isprovided for rotating the rolls 54. Each lehr roll 54 exerts a tractiveforce on the glass of sufficient magnitude to convey the glass throughthe lehr where its temperature is controlled to release permanent stressand strain in the glass. The rolls 54 constitute part of a means fortransporting newly formed float glass from the float bath chamber 47,through a vaporization coating chamber 55 and then through the annealinglehr 53.

The atmosphere within the bath chamber 47 is a reducing atmospherecontaining nitrogen and a small amount of hydrogen in order to insurethat oxidation of the molten metal 46 is inhibited. Generally theatmosphere contains about 90 to 99.9 percent nitrogen with the remainderbeing hydrogen. The atmosphere is maintained at a pressure slightlyabove ambient pressure, for example, 0.1 to 0.5 inch water tosubstantially prevent the ingress of ambient atmosphere into the bathchamber 47.

To retain the atmosphere and to permit the passage of the glass ribbonfrom the bath chamber 47, the exit end of the bath chamber is providedwith a series of curtains or drapes 56 which trail on the glass ribbonand serve as means for segregating the slightly pressurized atmosphereof the vaporization coating chamber 55 from the bath chamber 47. Thesedrapes or curtains 56 are usually made of flexible asbestos or fiberglass material which does not mar the glass and which withstandstemperature of the environment, namely, a temperature of approximately1000° to 1200°F. Additional drapes or curtains 57 of similar materialare provided at the entrance of the lehr 53, the latter drapes serve asmeans for segregating the lehr 53 from the vaporization coating chamber55.

The vapor coating chamber 55 is provided with vacuum hoods 58 havinginlets disposed both upstream, adjacent the bath chamber, anddownstream, adjacent the lehr. The vacuum hoods 58 extend verticallyupward to a pair of exhaust pipes 59 and are sufficiently spaced fromone another to provide sufficient room for supporting I-beams 60 and forthe vapor coating apparatus comprising vaporizer assembly 12 and vapordistribution assembly 13 along with associated equipment. The vacuumhoods 58 are movably supported on I-beams 60 by wheels 61 which rest onthe top of the I-beams 60. The I-beams 60 are disposed transverselyacross the path of the ribbon of glass 11 moving from the bath chamber47 to the lehr 53. The vacuum hoods are held in spaced relation by crossbrace 62. The exhaust pipes 59 are mounted on brackets 63 on which aremounted wheels 64 which rest upon tracks 65 of a supporting overheadbeam 66. The entire vacuum hood assembly comprising the vacuum hoods 58and exhaust pipes 59 may be moved transverse to the path of the glassribbon 11 to completely remove the assembly from the float line formaintenance and repair. This removal is accomplished by causing theassembly to move along beams 60 and 66 while rolling on the supportingwheels 61 and 64.

The vapor coater assembly is supported within the vapor coating chamber55 from I-beams 60 by means of vapor coater support bracket 67. Mountedon the support bracket 67 are vapor coater support wheels 68. Vaporcoater support wheels 68 rest on I-beams 60 one of which has a track 69mounted on it. The shape of the track 69 and of the support wheel 68engaging it is such as to prevent the lateral movement of the assemblywith respect to the track and I-beams.

The vapor coater assembly comprises, in addition to the vaporizerassembly 12 and the vapor distribution assembly 13, a mechanicalstructure for supporting these operative elements. This mechanicalstructure includes a motor 70 and jacks 71 for raising and lowering theassembly to position it closer to or farther from the substrate to becoated.

Depending from vapor coater support bracket 67 are vapor coater crossarms 72. Mounted on cross arms 72 are a motor support 73 and jacksupports 74. Mounted on the motor support 73 is the motor 70, preferablya DC variable speed motor. Connected to this motor 70 is a drive shaft75 which is in turn connected to screw jacks 71. Within each jack 71there is appropriate gearing for driving a screw shaft in a verticalmotion.

Screw shafts 76 connect with the drive shaft 75 through jacks 71connected to a gear. By driving the drive shaft 75 by motor 70 the screwshafts 76 are caused to move vertically to raise and lower the vaporcoating assembly. Mounted on the screw shafts 76 are yokes 77. Connectedto and depending from yokes 77 are support arms 78 which connect tocross plates 79.

Mounted on cross plates 79 is a vaporizer cradle support 80 to which isbolted or otherwise connected the vaporizer chamber 14.

As briefly described above, the preferred practice of this inventionrequires that a carrier gas, preferably air, be supplied to thevaporizer chamber 14 to mix with the atomized spray of coatingcomposition coming from the spray nozzle tips 19 to enhance the rate ofvaporization of the coating material and then to carry the mixturethrough the heater 32 to further heat the combination for ultimatedelivery to the substrate to be coated. The carrier gas is supplied tothe vaporizer from manifolds 26 which are preferably pipes mounted onthe assembly by brackets 27. Flexible tubing 28 is connected to thecarrier gas manifold 26 and directed through heating elements 29 toconnectors passing through the wall of the vaporizer chamber 14 andentering the space formed by air distribution plates 33 with the wall ofthe vaporizer chamber. Power is supplied to heaters 29 from anelectrical cable 81 which passes through a supporting distributionconduit 82 mounted on brackets 27 and 83.

The internal details of the vaporizer 12 which is preferably employed inthe practice of this invention are further described in the copendingapplication of John Sopko entitled "Coating Composition Vaporizer".

The structural characteristics of the presently preferred apparatus areapparent in FIGS. 2, 3 and 4. Unreacted or excess coating compositionvapors and the carrier gas discharged from the nozzle 43 toward thesubstrate 11 fill the vapor coating chamber 55. Unreacted vapors andgases are removed from the chamber by vacuum hood 58. In order tominimize or avoid the buildup of deposits on irregular structuralsurfaces which might result in deposits flaking off and dropping ontothe substrate 11 thereby causing defects the vapor coating assembly isencased within a vapor coater shield 84. The vapor coater shield 84 maybe provided with reinforcement plates 85. It is connected to the coaterassembly by being connected to cross plates 79. The cross plates, 79 asindicated before, are connected to the support assembly 78 and arefurther connected to the vaporizer cradle support 80. As alreadyindicated, the vaporizer chamber 14 is connected to the vaporizer cradlesupport 80. The cross plates 79 are provided with access holes 86. Thespace between the vapor coater shield 84 and the vapor manifold 38 ispreferably filled with a thermal insulation 87, such as mineral wool,asbestos or the like.

As shown in FIG. 3 the construction of a vapor coater assembly to spanthe entire width of a conventionally formed glass ribbon may be modular.Modular design is preferred for ease of maintenance and repair of theequipment. Individual vaporizer chambers 14 with appurtenent equipmentare connected together to form an assembly which spans the entire ribbonwidth.

While the vaporizer 14 may be modular in design, the vapor distributionmanifold 38 and the vapor nozzles 43 are preferably single units. Inthis way vapors are uniformly distributed across the width of thesubstrate which is to be coated.

Referring to FIGS. 5 and 6, the details of the vapor distributionmanifold and the vapor nozzles may be appreciated.

The coating vapors are uniformly distributed along the substrate by thevapor manifold of plenum 38. The structure of a particularly preferredplenum 38 and nozzle 43 combination may be appreciated from the enlargedviews of FIGS. 5 and 6. The transverse length of the plenum or manifold38, which spans the width of a glass ribbon to be coated, is muchgreater than the width of the manifold. For example, in order to coat aglass ribbon having a width of about 10 feet the length of the manifold,d shown in FIG. 6, will be approximately 10 feet as well. In general,the width of the manifold will be one foot or less.

The vapor manifold 38 comprises a plurality of vapor channels which areelongated and separated from one another at their exit ends but whichmeet in a common channel at their entrance. The plurality of couplings37 which bring vapors from the vaporizer 14 to the manifold 38 areconnected to the manifold 38 along this common channel entrance.

Each vapor channel 39 may preferably be constructed with at least twoopposing curves so that the path of travel of vapors passing through thechannel must change direction at least twice. In this manner theuniformity of vapor distribution along the length of the channel isenhanced. While baffles may be positioned within the channels to furtherinterrupt the vapor flow and distribute the vapor along the length ofthe channels, the simple design without baffles but with changed flowdirection is preferred. In the preferred design there are no areas ofstagnation and no protruding bodies to create eddy flows of significantmagnitude.

Surrounding the vapor channels 39 are cavities 41 and 42 for carrying aheating or cooling fluid as desired according to the cross current flowsas illustrated in FIG. 6. These chambers 41 and 42 extend along thelength of the vapor manifold 38 and are connected to a source of heatingor cooling fluid (not shown). In the preferred embodiment hot oil issupplied to the chambers.

Connected to the vapor manifold 38 are nozzle wall members 44 formingnozzles 43 which direct the vaporized coating composition and carriergas toward the substrate 11 which is to be coated. The nozzles 43 areelongated as seen in FIG. 6, and in plan view they appear as slots. Thecross-section of the nozzle openings viewed parallel to the major slotdimension, e, illustrates that the preferred nozzles narrow considerablyfrom their entrance to their exit. The contraction of each slot is suchthat vapor passing through the slot is continuously accelerated alongthe length of the slot. In this way the boundary layer of vaporsadjacent the slot wall is minimized, and the perimeter of the slot isuniformly wet by the vapors such that the exiting vapors are uniformlydirected against the substrate. The nozzles may be characterized by acontraction ratio, which is the ratio of inlet area to outlet area or inthe nozzles shown in FIGS. 5 and 6 as c/a. The preferred flow conditionsfor obtaining efficient and uniform coating are described below and theconditions described are defined as the conditions at the exit end ofthe nozzles. The preferred nozzles are the subject of the copendingapplication of Krishna Simhan entitled "Nozzle for Chemical VaporDeposition of Coatings".

The minor dimension of each nozzle exit, indicated as a in FIG. 5,dictates the spacing b between the nozzle exit and the substrate.Preferably the ratio b/a ranges from 0.75 to 10. In the most preferredembodiments the ratio b/a is from 1.25 to 5. Within the most preferredrange of spacing as indicated by the ratio b/a the rate of coatingdeposition is substantially greater than at closer or more distantspacings.

Each vapor channel 39 preferably has a volume of at least about sixminutes times the volumetric throughput of the channel. By having thiscapacity to hold up vapors passing through the channel the channelserves as a calming section to wash out in residual velocity variationsresulting from the flow of discrete streams exiting from the flexiblecouplings 37. As mentioned before, the vapor channels 39 preferablyreorient vapor flow tending to uniformly distribute the vapor along thelength of the manifold 38. The configuration and size of the vaporchannels 39 are observed to cooperate with the shape of the nozzles 43.If the contraction ratio, c/a, for the nozzles is increased,particularly above about 5 to 6, the capacity or volume of the vaporchannels 39 may be decreased without detrimental effect.

Each nozzle 43 is formed of two members 44, each having a curved face,connected to the manifold 38 with their curved faces in facingrelationship. Each member may be provided with a channel 45 for carryinga fluid, such as hot oil, to control the temperature of the vapors andgas being discharged. In the preferred embodiment hot oil passes throughparallel channels 45 and then through channels 41 and 42. Thetemperature of the oil to and from the nozzles may be measured, and thetemperature calculated from such measurements to be the nozzletemperature is the temperature employed in defining vapor flowconditions at each nozzle exit.

The curved surfaces defining the flow region of the nozzles are smoothlymachined to avoid creating minute obstructions or scratches that wouldimpart local disturbances to the vapor and gas flow. In a preferredembodiment nozzle members are made of machined steel or other basemetal, and the curved interior surfaces are plated with an easily workedmetal such as gold or other precious metal. A metal finish of at leastabout 64 microinch and preferably about 16 microinch is satisfactory.When the contraction ratio, c/a is sufficiently great the metal finishmay be less smooth without effect.

The curvature of the nozzle interior surfaces is such that the radius ofcurvature is least at the entrance and greatest (approaching infinity)at the exit. In a most preferred embodiment the radius of curvaturemonotonically (and preferably constantly) increases as a function ofdistance from the entrance toward the exit of the nozzle. For ease inthe construction of the apparatus the nozzle members 44 are machined todistinctly different radii in separate regions (I, II, III and IV forexample) along the path length of the nozzle. Each region is smoothlymachined to blend with the next.

The exit edges of the nozzle members are preferably sharp, well definedcorners so that the substrate facing portion of the nozzle members willnot be wet by exiting vapors and gas. The substrate facing edge of eachnozzle member 44 should be about 90° with respect to the face of themember and preferably will be about 87° so that the edge has an angle ofabout 3° up away from the nozzle exit with respect to the plane of thesubstrate.

The flow conditions which are maintained in the practice of thisinvention are defined at each nozzle exit. With reference to FIG. 5, thefollowing parameters are considered. The characteristic length employedin determining the vapor discharge Reynolds number is the hydraulicdiameter of the nozzle, defined as four times the nozzle cross-sectionalarea divided by wetted perimeter of the nozzle opening: ##EQU1## Since ais much less than e the hydraulic diameter approximates 2a. Thetemperature of the flowing vapor-gas mixture is considered to be theaverage oil temperature across the nozzle determined from measured inletand outlet oil temperatures. The density and viscosity of the vapor-gasmixture are determined to be the density and viscosity of the mixture atthe nozzle temperature and vaporization chamber pressure. In general theproperties of the carrier gas at that temperature and pressure aresatisfactory. The flow velocity is determined from the mass flow to thevaporizer divided by the density of the mixture as indicated furtherdivided by the total area of the nozzle exit openings (number of nozzlesmultiplied by [a .sup.. e]).

The following examples illustrate the importance of nozzle exit Reynoldsnumber and nozzle-to-substrate spacing.

EXAMPLE I

An experimental apparatus having a single nozzle like that describedabove having the following characteristics is employed for the testsdescribed below. The apparatus has a motor driven fan capable ofdelivering 3000 liter/minute of gas. A 5 kilowatt heating coil isprovided downstream of the fan with the heating coil located in the ductthrough which the gas flows from the fan to the nozzle. A thermocoupleis located in the wall of the duct immediately upstream of the nozzle,and this thermocouple is connected to a temperature regulator which isconnected to and controls the power to the heating coil. A substratesupport is positioned opposite the nozzle opening. The substrate supportis positioned opposite the nozzle opening. The substrate support isprovided with means for heating the substrate, and a series ofthermocouples are provided for monitoring substrate temperature. Thesupport is constructed to hold a flat substrate in a plane perpendicularto a plane defined through center of the nozzle along the axis ofdischarged gas flow.

An optical interferometer (MACH-ZEHNDER) is provided in surroundingrelation to the experimental apparatus. The interferometer is positionedso that the center of its line of sight is in the plane defined by theaxis of gas flow and is parallel to the plane of a substrate. Theinterferometer employs two coherent monochromatic light beams, eachhaving a wavelength of 546 nanometers (mercury arc lamp with narrow bandgreen filter). Since the anticipated flow fields to be studied exhibit asubstantial temperature gradient, a rotating mirror system is used inthe interferometer. A rotation rate providing for 200 orders ofinterference is employed. Optical interference is recorded using acamera, and the resulting photographs reveal temperature profiles by acomparison of fringe shifts in terms of fringe widths in accordance withthe well known principles of interferometry. As derived from theGladstone-Dale relationship, a shift of n fringe spaces indicates atemperature difference of n .Δθ where Δθ is the difference between thelocal temperature at the fringe and the reference temperature, θ_(R),which is the bulk carrier gas temperature detected under quiescentconditions.

The apparatus was operated first with a nozzle-to-substrate spacing oftwo times the nozzle width (one times hydraulic diameter). Heated airalone was discharged at several flow rates characterized as havingReynolds numbers of 900, 1500, 2000, 2500, 4000 and 5000.

The heated gas (air) which is discharged against the substrates mustturn 90° in the vicinity of the substrate. The beginning of this turn isobserved from the interferograms (the photographs of the interferedlight) to be about 0.8 times the nozzle width, a, above the substrate.At Reynolds numbers at and above 2500 a pronounced sharp boundary regionof uniform density is observed adjacent the substrate. This isindicative of uniform and efficient deposition conditions. Also at andabove a Reynolds number of 2500 the width of the effective flow contactwith the substrate is observed to be substantially greater than thenozzle width so that the coating reactants can be effectively spreadover the substrate surface.

The experiments when repeated with substrate temperatures ranging from930°F. to 1025°F. reveal no significant variation with substratetemperature.

The experiments are repeated with the nozzle-to-substrate spacingvaried. Spacing ratios of b/a = 4, b/a = 2 and b/a = 1 are tested.

For a spacing ratio of 4 the interferograms reveal gas density mapsexhibiting a sufficiently broad region of uniformity near the substratefor uniform coating at a Reynolds number of 5000. At lower Reynoldsnumbers the region is diminished and below a Reynolds number of about2500 the density map suggests the likelihood of non-uniform coating.

For a spacing ratio of 2 the interferograms reveal gas density mapsexhibiting a divergence of the flow into a uniform coating regionbeginning at about 0.67 times the nozzle width above the substrate. Atthis spacing ratio flow oscillations which were apparent at a greaterspacing ratio are absent and the flow and density fields remain uniformwith respect to time. Even below a Reynolds number of 2500 a smalluniform coating region is observed and above a Reynolds number of 2500the width of the region exceeds the nozzle width and at a Reynoldsnumber of 5000 the region width is about two times the nozzle width.

For a spacing ratio of 1 the interferograms reveal gas density mapsexhibiting sharply turning flows creating variable pressure fields. Thistends to destroy the effect of the discharge flow and the higherReynolds numbers within the preferred range are reached with a uniformcoating region still confined to about the width of the nozzle.

Further reduction of the spacing ratio requires higher Reynolds numbers.Despite any a priori thought that improvements might be made by movingthe nozzle closer to the substrate any boundary penetration which mightbe expected is found to be offset by non-uniform conditions observedexperimentally.

While the example described above establishes the significance ofReynolds number and nozzle-to-substrate spacing for vapor coatinginsofar as their significance may be deduced from gas density variationsand other conditions in the vicinity of a substrate, the example whichfollows describes coating a glass substrate according to the preferredembodiment of this invention.

EXAMPLE II

The apparatus shown and described above is positioned across a floatformed ribbon of glass between a float forming bath and an annealinglehr.

A continuous ribbon of clear glass approximately ten feet wide and about1/4 inch thick is conveyed beneath the device at a linear velocity ofabout 250 inches per minute. The glass is a conventionalsoda-lime-silica glass having a visible light transmittance of about 88percent.

A coating solution is prepared. The solution has the followingcomposition on a one gallon basis.

    ______________________________________                                        Iron acetylacetonate                                                                              510 grams                                                 Chromium acetylacetonate                                                                          150 grams                                                 Cobalt acetylacetonate                                                                             55 grams                                                 Methylene chloride   1 gallon                                                 ______________________________________                                    

The coating solution is delivered to the solution line 17 at a rate ofabout 0.2 gallon per minute, at a pressure of about 10 psig and at atemperature of about 70°F. Atomization air is supplied to theatomization gas line 23 at a pressure of about 5 psig and at atemperature of about 70°F.

Carrier ar is delivered to the carrier gas manifold 26 at about 38 psigand at a rate of about 170 SCFM. The carrier air is heated to about500°F. in the preheaters 29 and is delivered to the vaporizer chamber 14with the air velocity through the distributor plates 33 being about 5 to10 feet per minute. The sensible heat in the air is sufficient tovaporize the coating solution and to establish the resulting air-vapormixture temperature within the range of about 400°F. to 420°F.

Hot oil is supplied to all heaters at a temperature of about 410°F.Thus, the coating mixture leaving the vaporizer chamber 14 and passingthrough the plenum 38 and nozzles 43 has a stabilized temperature ofabout 410°F. The glass temperature beneath the nozzles is about 1050°F.

The nozzle-to-substrate spacing is b/a = 2. The described conditionsprovide a nozzle exit flow Reynolds number of 5000. The Reynolds numberis based on the viscosity of air at 410°F. and the density of theair-methylene chloride mixture at 410°F. and one atmosphere pressure.Mass flow is directly utilized from the known input.

The apparatus is operated for a period of 20 minutes to coat about 200square feet of glass. The resulting coating is uniform over the surfaceof the glass with the average visible light transmittance of the coatedglass being 40 percent and the variation of transmittance being lessthan ± 2 percent except for the extreme marginal edges of the glassextending beyond the major dimension of the nozzles.

The coating is observed to be more uniform and have a much more finelygrained appearance than coatings produced by spray methods using thesame coating materials.

EXAMPLE III

The method of Example II is repeated several times except that in eachinstance some process parameter is varied to determine its influenceupon the coatings produced.

First, the method is repeated with the exit flow having a Reynoldsnumber of 2500. The resulting coating is of excellent quality as inExample II although the overall average transmittance is only 50 percentindicating somewhat less coating or deposition efficiency than in thepreferred practice of the invention.

Second, the method is repeated with the exit flow having a Reynoldsnumber of 2000. The resulting coating is thinner and less uniform thanin the previous example; the average transmittance is only 60 percentwith the transmittance range being ± 5 percent which is unacceptable forarchitectural applications.

Third, the method is repeated with the exit flow having a Reynoldsnumber of 7000. The resulting coating is of excellent quality as inExample II.

Finally, two runs are made with the exit flow having a Reynolds numberof 5000. In one run the nozzle-to-substrate spacing is 0.9 times thenozzle width and in the other the spacing is 5 times the nozzle width.The resulting coating in each instance is sufficient to provide anoverall average transmittance of less than 50 percent but the variationin each instance is about ± 3 percent indicating marginal quality formany architectural uses.

We claim:
 1. An apparatus for applying a coating to a substrate bydirecting a gaseous mixture comprising at least one coating reactantthrough a nozzle against a substrate comprisinga. An enclosed chamberhaving inlet means for receiving a vaporizable coating reactant and agaseous carrier for mixing the coating reactant with the gaseous carrierto provide a resulting gaseous mixture at a specified first pressure, b.conduit means interconnecting said chamber and a nozzle for distributingthe resulting gaseous mixture to said nozzle, c. a nozzle comprising anelongated slot having an entrance end and an exit end that is smallerthan the entrance end and having interior surfaces of increasing radiiof curvature from the entrance end to the exit end to accelerate flow ofthe gaseous mixture adjacent the interior surfaces of the nozzle, d.said nozzle connected at its entrance to said conduit means fordirecting the resulting gaseous mixture against the substrate at asecond specified pressure less than the first specified pressure, e.said nozzle entrance and exit flow areas being sized for directing theresulting gaseous mixture at an exit Reynolds Number of at least about2500 when the resulting gaseous mixture exits said enclosed chamber atthe first specified pressure, and f. means for supporting a substrate infacing relationship to said nozzle exit whereby said coating is applied.2. The apparatus for applying a coating according to claim 1 whereinsaid means for supporting conveys the substrate in a path substantiallytransverse to the major dimension of said elongated slot.
 3. Theapparatus for applying a coating according to claim 1 wherein thesurfaces of said nozzle adjacent the interior faces of said nozzle atthe exit thereof form an angle less than about 90° with said adjacentinterior faces.
 4. The apparatus for applying a coating according toclaim 3 wherein said angle is about 87°.
 5. The apparatus for applying acoating according to claim 1 wherein said apparatus further comprisesmeans for positioning the exit of said nozzle from the facing surface ofsaid substrate a distance of at least 0.5 times the minor dimension ofsaid nozzle exit.
 6. The apparatus for applying a coating according toclaim 5 wherein the distance from said nozzle exit to the facing surfaceof a supported substrate is from about 1.25 to about 5 times the minordimension of said nozzle exit.
 7. The apparatus as set forth in claim 1wherein said substrate support means are provided in proximate relationto said nozzle exit end such that the centerline of gaseous flow fromsaid nozzle exit end is substantially normal to the principal plane of asupported substrate and the spacing from the exit end of said nozzle tothe facing surface of the supported substrate is at least about 0.5times the minor dimension of said nozzle exit end.
 8. The apparatus forapplying a coating according to claim 7 wherein the nozzle exitend-to-substrate spacing is from about 0.65 to about 5 times the minordimension of said nozzle exit end.
 9. The apparatus for applying acoating according to claim 7 wherein the nozzle exit end-to-substratespacing is from about 1.25 to about 5 times the minor dimension of saidnozzle exit end.
 10. The apparatus for applying a coating according toclaim 7 wherein said means supporting comprises means for conveying thesubstrate past said nozzle with (1) the major dimension of said nozzleslot substantially transverse to the direction of substrate conveyance,(2) the projection of the major dimension of said nozzle to a planenormal to both said substrate and to the direction of said substratetravel and (3) the major dimension of said nozzle being less than thewidth of said substrate normal to the direction of travel of saidsubstrate.
 11. The apparatus for applying a coating according to claim 7wherein the nozzle exit end-to-substrate spacing is from about 1.25 toabout 5 times the minor dimension of said nozzle exit and saidcombination is provided with means for distributing said gaseous mixturesubstantially uniformly to said nozzle along its major dimension. 12.The apparatus for applying a coating according to claim 7 wherein saidnozzle is provided with means for maintaining the temperature of saidgaseous mixture flowing therethrough.
 13. The apparatus as set forth inclaim 10 wherein said conveying means are mounted between an exit end ofa forming chamber and an entrance end of an annealing lehr.
 14. Theapparatus as set forth in claim 1 wherein the exit Reynold's number isabout 5,000.